This invention is a further development in the standing-wave linear charged particle accelerator art. More specifically the invention is an improvement upon the side-cavity coupled accelerator configuration as described by E. A. Knapp, B. C. Knapp and J. M. Potter in an article entitled "Standing Wave High Energy Linear Accelerator Structures", 39 Review of Scientific Instruments 979 (1968); and as further described in U.S. Pat. No. 3,546,524 to P. G. Stark.